I don't think it deserves to be classified with or compared to direct stimulants like amphetamine or caffeine - it has as much in common with those as melatonin does with temazepam or nitrazepam.
If you're looking for direct stimulation or any kind of recreational effect, it's useless. What it's excellent for is wiping away the effects of fatigue. Say you had a late night, only got 2 or 3 hours of sleep and you feel awful and foggy, but you have to get up and go about your day doing tasks that require energy and concentration, that's where modafinil comes in handy. You pop the pill, and once it kicks it you'll feel like you had a full 8 hours of sleep the night before. That's what it's for, wiping away the effects of fatigue. There is a mild stimulant component the first few times you use it (comparable to maybe 2.5 - 5mg d-amp in potency, but without any euphoria, just a bit of tweakiness and jaw clenching), but 90% of that goes away after 2 - 3 times you use it, and you're just left with the wakefulness inducing effect. There doesn't seem to be any real tolerance buildup to the wakefulness effect, at least I experienced none in the 3 months I took it daily.
Great for functioning when fatigued, non-addictive, non-recreational. Worst side effects are insomnia if you take it after early afternoon, occasional headaches and, if you use it daily for too long, some mild anxiety. And obviously using it as an excuse to not get a proper nights sleep every night for long periods of time is going to be harmful to your body and result in an excess of fatigue when you stop taking the pills.
